1. Field of the Invention
The present invention relates, in general, to an electric motor in which a permanent magnet is embedded into a rotor, and more particularly, to an interior permanent magnet synchronous motor in which a feature of a V-type recess formed in the rotor is improved so as to significantly reduce torque ripple and resultant noise at a low speed.
2. Description of the Related Art
Recently, due to the growing concern regarding the overuse of fossil fuels, high efficiency, high performance electric devices have been receiving much attention. Among them, eco-friendly vehicles such as electric cars, hybrid electric cars, and the like have been developed for the purpose of reducing gas emission. For use in such eco-friendly vehicles, an interior permanent magnet synchronous motor is typically used and consistent attention is given to improving their overall cost and operation. The structure of such an interior permanent magnet synchronous motor is such that a permanent magnet is embedded into a rotor. Such motors require high torque and low torque ripple, and are provided by systematic, optimized designs.
However, in such a conventional interior type motor, torque ripple at low speed causes high frequency noise to be generated, degrading quality of a product. Thus, there is a need for a structure in which, upon regenerative braking at a low speed, torque ripple is reduced so as to reduce noise.
As a solution to this problem, a rotor for a hybrid driving motor has been provided. In this motor, an annular body is arranged inside a stator having a core around which a power feeding coil is wound. A permanent magnet unit is embedded into the annular body and has a pair of separate left and right permanent magnets, and a U-type sectional groove is recessed into a portion of the annular body in which the pair of permanent magnets are not embedded. However, this technique does not reduce high frequency noise caused by torque ripple at a low speed in the motor, and thus there is still a need to provide a motor that reduces high frequency noise.
The description regarding the related art is provided only for understanding of the background of the invention, so it should not be construed by ordinarily skilled persons in the art to be admitted to be the related art.